Acronym2
'Cedo Alteram'
People of CivFanatics: Steam is nothing to worry about! I have used Steam for 3 years and never had a problem with it (Except for one time I got a keylogger, but Steam support fixed that for me and I was playing just fine again.) It gives you a community, automatic updates, and lots and lots of free features for both the developer and the consumer. Plus, Steam often hosts insane sales. (19 THQ games for 50$, for example.)
Look, I'm not neccessarily trying to bash Steam. (These Steam debates sometimes get a little heated.) However, you don't consider a keylogger nothing to worry about? That is perhaps one of the worst infections a computer can get! A keylogger can be used to easily steal credit/debit card numbers, pin numbers, account information, personal information, etc,etc............it records every keystroke you make on your machine in a file that is sent to or accessed by the attacker!
As I said earlier, I'm not neccessarily knocking Steam, but if it was a contributing factor to your keylogger infection, it is of concern. It seems that if Steam technical support helped you to remove the keylogger than Steam might have had something to do with its transmission to your machine.
Nobody here has yet entered into an inteligent debate about Steam with regard to its technical functioning when it comes to security, what permissions it has over our systems and such. Steam, in part, will function as a web browser and instant messenger along with a DRM capability as well as initiate transactions. The Steam Subscriber Agreement specifies (among other things) that they will not be held liable for damage and loss resulting from viruses contracted through the use of Steam.
The fact that Steam has so many users and will, apparently, be adding many more makes it a very attractive target. I do not think it unreasonable or "fear mongering" to merely raise the queston of security.